Temperature control of refrigeration cavities with a variable speed compressor and a variable speed evaporator fan
A refrigeration appliance includes a refrigeration circuit with a variable speed compressor, an evaporator, and a variable speed evaporator fan. A controller is operatively connected to the refrigeration circuit and is programmed to calculate a heat load ratio as a ratio between the difference between the ambient temperature and the set point temperature of the fresh-food compartment and the difference between the ambient temperature and the freezer compartment reference point; calculate a speed of one or both of the variable speed compressor and the variable speed evaporator fan as a function of the calculated heat load ratio; and operate one or both of the variable speed compressor and the variable speed evaporator fan at the calculated speed. A method of controlling temperature in cavities of a refrigerator is also provided.
1. A refrigeration appliance, comprising:
a fresh-food compartment configured for storing food items at a first target temperature above zero degrees Celsius;
a freezer compartment configured for storing food items at a second target temperature below zero degrees Celsius;
a refrigeration circuit configured for cooling the fresh-food compartment and the freezer compartment, the circuit having a variable speed compressor, an evaporator, and a variable speed evaporator fan; and
a controller operatively connected to the refrigeration circuit and programmed to:
determine a difference between an ambient temperature and a set point temperature of the fresh-food compartment;
determine a difference between the ambient temperature and a freezer compartment reference point;
determine a difference between an ambient temperature value higher than an expected normal ambient temperature and the freezer compartment reference point;
determine a difference between the ambient temperature value higher than the expected normal ambient temperature and a fresh-food compartment reference point;
calculate a current heat load as a ratio between the difference between the ambient temperature and the set point temperature of the fresh-food compartment and the difference between the ambient temperature and the freezer compartment reference point;
calculate a second heat load as a ratio between the difference between the ambient temperature value higher than the expected normal ambient temperature and the freezer compartment reference point and the difference between the ambient temperature value higher than the expected normal ambient temperature and the fresh-food compartment reference point;
calculate a speed of one or both of the variable speed compressor and the variable speed evaporator fan as a function of the calculated current heat load and the second heat load; and
operate one or both of the variable speed compressor and the variable speed evaporator fan at the calculated speed of the variable speed compressor and the variable speed evaporator fan, respectively.
2. The refrigeration appliance of claim 1 , wherein the ambient temperature is determined based on a measurement by an ambient temperature sensor.
3. The refrigeration appliance of claim 1 , wherein the ambient temperature is determined virtually by an estimation based on a response to a thermal load of the refrigerator.
4. The refrigeration appliance of claim 1 , further comprising a cooling air channel between the fresh-food compartment and the freezer compartment, wherein the cooling air channel between the fresh-food compartment and the freezer compartment is formed as a fixed cooling air channel.
5. The refrigeration appliance of claim 1 , wherein the set point temperature of the fresh-food compartment is based on user input via a user interface.
6. The refrigeration appliance of claim 1 , wherein the freezer compartment reference point is a reference parameter determined through simulation and/or laboratory testing with a value between −30 and 10.
7. The refrigeration appliance of claim 4 , wherein dimensions of the cooling air channel between the fresh-food compartment and the freezer compartment are controlled by a manual damper configured to be operated by a user.
8. The refrigeration appliance of claim 4 , wherein the controller is further programmed to adjust cooling capacity distribution between the fresh-food compartment and the freezer compartment based on the calculated speed of at least one of the variable speed compressor and the variable speed evaporator fan.
9. The refrigeration appliance of claim 4 , wherein the controller is further programmed to adjust relative quantities of airflow to the fresh-food compartment and the freezer compartment, respectively, based on the calculated speed of at least one of the variable speed compressor and the variable speed evaporator fan.
10. The refrigeration appliance of claim 1 , wherein the controller is a proportional integral (“PI”) or a proportional-integral-derivative (“PID”) controller programmed to increase a working speed of at least one of the variable speed compressor and the variable speed evaporator fan above the calculated speed of at least one of the variable speed compressor and the variable speed evaporator fan in response to door openings, warm loads, and high ambient temperatures.
11. The refrigeration appliance of claim 1 , wherein the controller being programmed to calculate the speed of one or both of the variable speed compressor and the variable speed evaporator fan as the function of the calculated current heat load (HL_current) includes the controller being programmed to calculate the speed of one or both of the variable speed compressor and the variable speed evaporator fan as a function of a heat load ratio HL_ratio, wherein the controller is programmed to calculate the heat load ratio HL_ratio using a formula:
HL_ratio
=
HL_current
HL_ref
_High
wherein:
HL_current
=
T_amb
_measured
-
Ref_FZ
T_amb
_measured
-
Ref_FF
HL_ref
_High
=
T_base
_amb
_High
-
Base_FZ
T_base
_amb
_High
-
Base_FF
,
wherein T_amb_measured is the ambient temperature, Ref_FZ is a reference for speed calculation equal to the freezer compartment set point, Ref_FF is the set point temperature of the fresh-food compartment, T_base_amb_High is a reference value selected as the value higher than the expected normal ambient temperature, Base_FZ is a reference for speed calculation equal to the freezer compartment reference point, and Base_FF is a reference for speed calculation equal to the fresh-food compartment reference point.
12. The refrigeration appliance of claim 10 , wherein the controller is programmed to calculate the speed of at least one of the variable speed compressor and the variable speed evaporator fan in discrete or continuous time intervals as a linear or non-linear function of the calculated heat load ratio HL_ratio, wherein respective speed of the variable speed compressor and the speed of the variable speed evaporator fan equations are determined in simulation or laboratory testing through curve fitting as follows:
comp_rpm_min= f (HL_ratio)
fan_RPM_evap_min= f (HL_ratio).
13. A method of controlling temperature in cavities of a refrigerator cooled by a refrigeration circuit having a variable speed compressor, an evaporator, and a variable speed evaporator fan, the method comprising the steps of:
determining an ambient temperature;
determining a difference between the ambient temperature and a set point temperature of a fresh-food compartment;
determining a difference between the ambient temperature and a freezer compartment reference point;
determining a difference between an ambient temperature value higher than an expected normal ambient temperature and the freezer compartment reference point;
determining a difference between the ambient temperature value higher than the expected normal ambient temperature and a fresh-food compartment reference point;
calculating a current heat load as a ratio between the difference between the ambient temperature and a set point temperature of the fresh-food compartment and the difference between the ambient temperature and a freezer compartment reference point;
calculating a second heat load as a ratio between the difference between the ambient temperature value higher than the expected normal ambient temperature and the freezer compartment reference point and the difference between the ambient temperature value higher than the expected normal ambient temperature and the fresh-food compartment reference point;
calculating a speed of one or both of the variable speed compressor and the variable speed evaporator fan as a function of the calculated current heat load and the calculated second heat load; and
operating one or both of the variable speed compressor and the variable speed evaporator fan at the calculated speed of the variable speed compressor and the variable speed evaporator fan, respectively.
14. The method according to claim 13 , wherein the ambient temperature is determined based on a measurement by an ambient temperature sensor.
15. The method according to claim 13 , wherein the ambient temperature is determined virtually by an estimation based on a response to a thermal load of the refrigerator.
16. The method according to claim 15 , wherein the ambient temperature is determined virtually as a linear approximation by measuring a temperature in the fresh-food compartment during an off cycle of the variable speed compressor.
17. The method according to claim 13 , further comprising adjusting relative cooling capacity to the fresh-food compartment and the freezer compartment, respectively, based on the calculated speed of at least one of the variable speed compressor and the variable speed evaporator fan.
18. The method according to claim 13 , wherein the set point temperature of the fresh-food compartment is based on user input via a user interface.
19. The method according to claim 13 , wherein the freezer compartment reference point is a reference parameter determined through simulation and/or laboratory testing with a value between −30 and 10.
20. The method according to claim 13 , further comprising selecting a reference parameter HL_ratio related to the speed of at least one of the variable speed compressor and the variable speed evaporator fan, wherein the reference parameter HL_ratio is proportional to a ratio between the current heat load and a ratio between a difference between the ambient temperature value higher than the expected normal ambient temperature and the cavities' reference points.
21. The method according to claim 20 , wherein the reference parameter HL_ratio is calculated using a formula:
HL_ratio
=
HL_current
HL_ref
_High
wherein:
HL_current
=
T_amb
_measured
-
Ref_FZ
T_amb
_measured
-
Ref_FF
HL_ref
_High
=
T_base
_amb
_High
-
Base_FZ
T_base
_amb
_High
-
Base_FF
,
T_amb_measured is the determined ambient temperature, Ref_FZ is a reference for speed calculation equal to the freezer compartment reference point, Ref_FF is the set point temperature of the fresh-food compartment, T_base_amb_High is the ambient temperature value higher than the expected normal ambient temperature, Base_FZ is a reference for speed calculation equal to the freezer compartment reference point, and Base_FF is a reference for speed calculation equal to the fresh-food compartment reference point.
22. The method according to claim 21 , wherein the controller calculates the speed of at least one of the variable speed compressor and the variable speed evaporator fan in discrete or continuous time intervals as a linear or non-linear function of the calculated heat load ratio HL_ratio, wherein respective speed of the variable speed compressor and the speed of the variable speed evaporator fan equations are determined in simulation or laboratory testing through curve fitting as follows:
comp_rpm_min= f (HL_ratio)
fan_RPM_evap_min= f (HL_ratio).
23. The method according to claim 13 , further comprising increasing a working speed of at least one of the variable speed compressor and the variable speed evaporator fan above the calculated speed of at least one of the variable speed compressor and the variable speed evaporator fan in response to door openings, warm loads, and high ambient temperatures.